Window perf is a calendared adhesive-backed PVC vinyl that is perforated with a pattern of round, evenly spaced holes. The advantage of window perf is that it allows graphics printed on a glass surface, such as windows, to be seen from the outside, but appear invisible to the people inside looking out. Window perf is sometimes called “see-through vinyl,” or “one-way vision film,” but the basic concept is the same.
In most cases the actual size of the holes are uniform (usually about 1.5mm). It’s the distance between the holes that determines the print coverage vs. visibility. For example, 50/50 window perf film means that 50 percent of the material is printable area and 50 percent is perforation. Window perf comes in a number of different hole configurations; 50/50, 60/40 and 70/30 are the most common. The first number in this designation represents the amount of printable area and the second number represents the amount of open (see-through) area. Therefore, a 70/30 window perf has a larger printable area, but less see-through area, than a 50/50 window perf.
Window perf is made in layers—a white printable top layer, a black layer, an adhesive layer and a release liner. The black layer enhances see-through visibility from behind the print. (Image courtesy Continental Grafix)
Film Construction and Applications
Window perf is made in layers. The first (top) layer is the white vinyl that is printable, the next layer is black vinyl, followed by an adhesive coating and finally the release liner. The black layer acts as an optical illusion that allows clear visibility from behind the printed vinyl, but works best when you have 70 percent or more of the light on the printed side.
Typical applications for window perf include vehicle windows (side and rear), exterior edifice glass (i.e. building wraps), retail window displays, and any situation where you want a graphic to be seen from one side, but not from the other. Vehicles are by far the most common use for window perf, but building wrap windows are very common in places such as Las Vegas.
In most applications that are not vehicle related, you would not typically laminate the window perf. However, for vehicle applications some people laminate and some don’t. This is a choice you should research for your particular application, and decide what is best for your clients.
Some people think you can use window perf to separate two rooms that are divided by glass—like a conference room with glass walls. However, you generally cannot achieve privacy in the room with window perf because the amount of light is typically the same inside and outside the glassed-in room. If the amount of light inside the room is greater than outside, then the film will appear more or less invisible.
The challenge for many shops is to find a window perf product that can be easily installed on the inside of the glass. Years ago 3M introduced a product for the Scotchprint 2000 electrostatic printing system where you could transfer the image onto a special perforated vinyl that had the adhesive on the face of the clear film. This allowed the digital print market to offer a reverse-mount window perf product.
Perforated window film used on retail shop windows such as this, can present graphics that can be clearly seen from outside, yet offer an unobstructed view from inside. (Images courtesy Clear Focus)
Today, Contra Vision offers an inside-mount perforated film called TT. It consists of black on white backing layers, and is a thermal transfer product that enables see-through window graphics for application to the inside of a window. The material is self-wound with the coating on the inside. The coating is transferred to a reverse-imaged, clear perforated material by a heated roller laminator and the liner is removed so that, when applied to a window, the image is visible right-reading from the outside and the black faces inside for good through vision.
Clear Focus offers another solution for inside-mounted window perf called PosterView. It is a non-adhesive film that you would print to the face (same as you would for normal window perf), then use a double-sided tape around the edge to attach to the glass, or use a full adhesive coverage by using an optically clear mounting adhesive product with permanent adhesive on one side and removable adhesive on the other. Using a laminator you apply the permanent adhesive side of the material to the image side of the PosterView, then remove the release liner and mount the graphic to the inside of the glass.
Interior-mount window perf employing similar mounting concepts are starting to become more readily available. Check with your preferred window perf manufacturer to see if they also offer this type of film.
This window perf graphic, was printed by Grellner Distributing, Sedalia, Mo., on a water-based printer using LexJet Aqueous Perforated Vinyl. (Image courtesy Lexjet)
Some of today’s vinyl window perf film manufacturers also offer a more economical version of their product. These types of “econo-films” are generally manufactured using only monomeric plasticizers (as opposed to films using monomeric in conjunction with other types of plasticizers).
The advantage to this product is that it costs much less than premium window perf. You can save yourself and your client some money by going this rout. The downside (there’s always a downside) is that over time vinyl films made with only monomeric plasticizers will shrink and crack, resulting in long-term failure.
That said, this type of economical window perf is ideal for short-term applications. The question then remains: How short is short-term? My recommendation is never more than two years. Check with the film manufacturer for recommended graphic life expectations for this type of film. Remember, saving money is always good, but it’s also true that you get what you pay for.
Installing window perf is very different than other kinds of vinyl film installations because of the film’s perforations. An optically clear overlaminate is usually recommended for outdoor window perf applications, because without a laminate the holes in the vinyl will fill with water and dirt, which will drastically reduce visibility and defeat the purpose of the media.
The number of perforations in a window film determine how much surface area is printable and how much is not. A 50/50 film offers 50 percent printing area while a 60/40 film offers 60 percent printable area. (Image courtesy Clear Focus)
If you are installing window perf that has been laminated you should install it the same way you would install normal vinyl—that is, you install from the center out to the edge, holding the squeegee at a 45-degree angle to the vinyl and pushing the vinyl down onto the surface—like you were plowing snow.
With un-laminated window perf you should not hold the squeegee this way as it will tend to catch the holes in the perf and rip the vinyl. Instead, hold the squeegee so that you drag it across the vinyl while you hold the vinyl off the surface. Or, you can hold the squeegee down at a very low angle, almost like it is flat on the vinyl. This makes it much less likely to catch the holes.
When applying window perf to a vehicle, many installers recommend finishing the edges with an edge sealer, or with thin strips of laminate to prevent lifting, especially if the window will be rolled up and down. I never recommend using application fluid to install window perf.
In closing, I will say that the unique properties of window perf are very attractive to many of my clients, and I make a lot of money using window perf as a marketing solution for the businesses I work with. I look forward to every window perf job I get. Good luck, be smart with your money, and I’ll see you on the show floor!